Abstract 4146800: A Retrospective Analysis of Measured Versus Estimated Resting Oxygen Uptake for Derivation of Fick Cardiac Output in Patients in the Cardiac Intensive Care Unit

Background: Estimated cardiac output using the Fick principal (estFickCO) frequently informs clinical decision making in Cardiology Intensive Care Units (CICU). Assessment of estFickCO relies on estimation of resting oxygen uptake (rVO 2 ). We hypothesized that large variance will be present between rVO 2 measured with a metabolic cart and the estimated rVO2 often used in CICUs. Methods: In this single-center study, 275 CICU patients with pulmonary arterial catheters in place to guide heart failure management underwent breath-by-breath metabolic cart measurement of rVO 2 for 10 minutes coupled with duplicate measures of arterio-venous oxygen content to derive Fick CO. Four equations to estimate rVO 2 were evaluated: weight-based only (3.5ml/kg/min, 1 MET); accounting for sex and BSA (Dehmer); sex, BSA, and age (Bergstra); and sex, BSA, age, and heart rate (LeFarge). Bland-Altman analysis and derivation of coefficients of variation were performed to evaluate the agreement between each equation and actual measured rVO 2 . Results: In this cohort of 275 patients (age 57.8±14.4, 24% female, BMI 28±6.9 kg/m 2 ) the mean measured rVO 2 was 276±71 mL/min and Fick CO was 4.7±1.6 L/min. Using 1 MET to estimate rVO 2 equated to a mean rVO 2 of 292±81 mL/min, the Dehmer equation estimated a mean rVO 2 of 283±49 mL/min, Bergstra estimated a mean rVO 2 of 248±37 mL/min, and the LaFarge equation estimated a mean rVO 2 of 239±53 mL/min. The frequency of error being >25% was calculated at 24%, 15%, 17%, and 19% respective to each equation. When analyzed using Bland-Altman plots, the Dehmer equation demonstrated the lowest mean bias as well as the lowest coefficient of variation when compared to the other three estimates ( Figure ) yet limits of agreement span VO 2 values associated with > 3 L/min differences in Fick CO across all 4 estimates. Conclusion: Measured VO 2 varies significantly from estimated VO 2 among CICU patients. Accounting for sex and BSA with use of the Dehmer equation was associated with the closest approximation of actual VO 2 values among 4 estimates analyzed in our study. High variance in rVO 2 estimates and impacts on management should be considered when interpreting estFickCO in CICU patients.